This invention relates to a novel process for the separation of high boiling oxygenated compounds from mixtures with phenol and/or cresol. The process is especially suitable for separating mixtures of phenol and aryl ketones such as acetophenone. The process is an extractive distillation process that employs substituted phenols and/or substituted cresols as extractive solvents in order to separate phenol and/or cresol from the high boiling oxygenated compounds.
U.S. Pat. No. 4,187,152 discloses a method for separating alkanols, alkanones, cycloalkanols and/or cycloalkanones from mixtures with phenol and/or cresol by distilling said mixtures in the presence of an extractive solvent comprising an alkylated, unmodified cycloalkyl, or aryl derivative of cyclohexanone or cyclohexanol.
U.S. Pat. No. 2,583,412 (Carlson et al.) discloses a method for separating mixtures of close-boiling oxygenated compounds, and particularly low molecular weight close-boiling alcohols, by distilling said mixtures in the present of a large excess of phenol.
Carlson et al. teaches that the volatility of compounds having 1 to 5 carbon atoms in neutral oxygenated mixtures with other oxygenated compounds, all compounds with normal boiling points below 105.degree. C., can be enhanced by the addition of phenol which has a normal boiling point of 180.degree. C. The invention of Carlson et al. discloses the separation of ideal mixtures of oxygenated compounds. For example, mixtures comprising ethanol and isopropanol ae separated by Carlson et al. by enhancing the volatility of ethanol over that of ispropanol. Also, Carlson et al. discloses the separation of mixtures of oxygenated compounds that exhibit positive deviations from ideal mixing such as the separation of ethanol from methyl ethyl ketone. In the first example of Carlson et al., the volatility of ethanol is enhanced only slightly from about 1.16-1.10 to about 1.28-1.38 by subjecting the original mixture to extractive distillation procedures with phenol as the extractive solvent.
The process of the present invention accomplishes separation of acidic phenolic molecules from their mixtures with high molecular weight neutral oxygenated compounds such as alcohols and ketones. The mixtures which may be easily separated by the process of this invention typically exhibit negative deviations from ideal mixtures, and the high molecular weight oxygenated compound of the mixture has at least seven carbon and a boiling point of at least about 175.degree. C.
The process of the present invention is especially suitable for separating mixtures of phenol and aryl ketones such as acetophenone. Mixtures comprising phenol and acetophenone are present in various industrial streams, as for example, in certain streams during the production of phenol by the partial oxidation of cumene. Mixtures of phenol and acetophenone may not be separated by simple distillation procedures due to the formation of a phenol-acetophenone maximum boiling azeotrope. By employing the process of this invention, the volatility of phenol relative to that of acetophenone may be enhanced from a value smaller than unity (i.e., 0.6 or lower) to a value of about 2.3. It is believed that the present invention represents a practical and economical method for obtaining acetophenone-free phenol and phenol-free acetophenone from their mixtures.